Truth on the Ground: Accurate, Repeatable GNSS/INS Simulations for Ground Vehicles


A vehicle’s design and its GNSS/INS implementation can have an influence on reception and navigation performance — especially in high-dynamic motion scenarios. Previously, we looked at the simulation implications for vehicles in flight as well as vessels at sea. In this post, we will cover GNSS simulations for ground vehicles.

Faithfully modeling ground vehicle GNSS reception

Digitally modeling the physical world always requires compromises. Model things accurately and you get simulations that produce useful results consistently. In our earlier articles, we explained why the placement of antennas and GNSS receivers with respect to a vehicle’s center of gravity (CG) must be modeled correctly in simulation. Assuming placement at the CG will introduce small errors that produce misleading results or simulation failures.  Although the distances may be smaller than on a ship or aircraft, the same is true for ground vehicle simulations.

Differences in the physics of motion also impact simulation fidelity. A moving ground vehicle’s GNSS antennas change orientation relative to overhead GNSS satellites — but not in the same way other vehicle types do. Flight simulations must account for the way aircraft roll during turns. Ground vehicles, on the other hand, make uncoordinated turns without rolling. Again, not modeling these differences results in errors in the simulated signal that compound over time.

Finally, simulations may need to account for conditions on the ground. Trees, buildings, and terrain can disrupt signals from one or more GNSS satellites. Natural and urban interference, as well as active jamming, can further degrade GNSS reception. When tests require this level of realism, you need simulator systems that are easily configured to model terrain obscuration and interference.a

Handling simulation complexity

Having the right algorithms to create high-fidelity models of moving ground vehicles is not enough to produce useful simulations. The underlying performance of the simulation system is just as important. In GNSS/INS simulations, for example, the output of the simulated GNSS and INS units must be coincident. That is, the GNSS and INS outputs for each point in simulated time must arrive together. Any senescence between the two can cause erroneous navigation performance.

CRPA testing is another area where simulator performance can undermine results. In the real world, signals from GNSS satellites and interference sources are phase-coherent for each antenna element. In simulation, you don’t get that for free. Simulator solutions must produce phase coherent outputs for every antenna element contained in the antenna manifold.

Choose the right simulation solution for accurate, repeatable GNSS simulations

Whether testing GNSS performance for vehicles in flight, at sea, or on the ground, CAST Navigation solutions have a forty-year track record of producing accurate, repeatable results. Intuitive graphical interfaces let you design high-fidelity simulations that accurately model the GNSS reception of vehicles traversing varied terrain. Precise, coherent wavefronts let you subject phased array antenna systems to complex interference simulations. Our modular system design approach lets you combine simulation capabilities for the specific needs of your project while giving you the scalability to meet future requirements.

Learn how CAST Navigation’s tailored solutions can improve your GNSS, INS, CRPA, and Jamming simulation needs.

June 30, 2022